Field of the Invention
The present invention relates to a microwave oven having a heater cooking function and is equipped with a damper which is actuated by the heat in the heating chamber to control ventilation to the heating chamber, or more specifically to an operation control system for a blower which cools the heating chamber exterior and electric components such as a magnetron.
A multi-functional microwave oven having heater cooking and microwave cooking functions is equipped with a damper that shuts off ventilation to the heating chamber to minimize heat loss during heater cooking operation and which allows ventilation to the heating chamber to release steam generating from cooked food to outside the heating chamber during a microwave heating operation.
For this application, the industry has recently proposed a damper that opens or closes due to the shape memory effect of a shape memory alloy. The damper using a shape memory alloy is disclosed in U.S. Pat. No. 4,608,474, issued on Aug. 26, by Kenichi Kohka, U.S. patent application Ser. No. 016,479, filed on Jan. 30, 1986, by Takeo Nakanishi, and U.S. patent application Ser. No. 484,460, filed on Apr. 13, 1983, by Masanobu Tanigawa.
However, any of the conventional commercialized dampers using a shape memory alloy utilizes a heater installed adjacent the shape memory alloy or the heat generated in the alloy itself when it is supplied with power, as a heat source for the alloy. The conventional damper of this type involves an additional electric heating device for actuating the damper, resulting in complicated construction and therefore high cost.